No, PSU sizes vary—ATX, SFX/SFX‑L, TFX, and Flex ATX have different dimensions and clearances.
Power supplies share a job, not a shell. The metal box at the back of a desktop can change in width, height, and depth based on its form factor and wattage. That means two units with the same power rating can fit in different ways inside a case. If you came here asking whether all PSUs are the same size, the answer is no—fit depends on the form factor, the model, and your case.
PSU Size Basics And Why It Varies
Size comes from a standard and from the design choices inside the unit. A form factor sets width and height so it can bolt into a case cutout. Depth is the wild card. Extra cooling, bigger transformers, or large modular boards can extend the body by a couple of centimeters. That extra length can collide with a shroud, drive cage, or a bottom fan if you don’t plan for it.
Form Factor Sets Width And Height
Desktop builders run into a few shapes often. ATX is the big one for mid‑towers and full towers. SFX and SFX‑L fit small cases. TFX and Flex ATX live in slim desktops, 1U gear, and tight OEM boxes. Each one locks in the faceplate size and the screw pattern so it lines up with the rear of the chassis.
Depth Varies By Model And Wattage
Depth is where models diverge. A common ATX unit starts around 140 mm deep. High watt models stretch to 160, 170, 180, or even 200 mm. SFX sits near 100 mm deep, while SFX‑L adds length to about 130 mm. Shorter Flex ATX models still need room for cables, so the case space behind the PSU matters more than the metal length alone.
Mounting And Bracket Options
If your case lists only ATX, you can still run an SFX unit with a simple steel adapter plate. Plenty of cases include one in the box. If yours doesn’t, third‑party brackets are cheap and sturdy. The reverse is not true: an ATX unit will not fit an SFX bay. TFX and Flex ATX use their own hole patterns and won’t swap with ATX without a custom mount.
Are All PSUs The Same Size: Form Factors And Fit
Here’s a quick tour of common desktop PSU shapes and how they fit. The numbers below are typical, not strict limits. Always check the product page and your case manual before you commit.
ATX Power Supplies
ATX sets a face width of about 150 mm and a height of 86 mm. That face mates to the rear of the case and uses a square fan grill on many models. The length front to back has range. Many mid‑range units sit near 140–160 mm deep. High power units can go longer. When you pick an ATX model, measure the space from the rear wall to the first thing in the way: a shroud edge, a drive cage, a reservoir, or a bottom intake fan.
SFX And SFX‑L
SFX drops the shell to about 125 mm wide and 63.5 mm tall, with a 100 mm depth on most units. It’s the go‑to for mini‑ITX builds. SFX‑L keeps the same width and height but stretches depth to roughly 130 mm. That extra 30 mm opens room for a larger, quieter fan and bigger internals. Many ATX cases accept SFX with a bracket, which frees space for excess cables and improves airflow around the GPU.
TFX And Flex ATX
These slim shapes show up in low‑profile cases and rack gear. TFX runs near 85 mm wide, 65 mm tall, and 175 mm deep. Flex ATX is even slimmer at around 81.5 mm wide, 41 mm tall, and 150 mm deep. Both use narrow blowers and tight cable bays, so check plug room with care. Builders reach for these only when the case demands it.
ATX12VO And The Old 24‑Pin
ATX12VO shifts the motherboard connector to a 10‑pin and moves 3.3 V and 5 V rails onto the board. It changes cabling and power behavior, not the outer shell. An ATX12VO PSU still follows the same physical form factor, so case fit rules don’t change. Just make sure your motherboard matches the connector style.
Measure Your Case And Plan Clearance
Tape measure out? Good. A quick set of checks can save a return label and a weekend teardown.
How To Measure PSU Space
- Rear opening: Confirm the cutout matches ATX, SFX, TFX, or Flex ATX. Look for the screw pattern in the manual.
- Depth room: Measure from the rear wall to the first obstruction. Subtract 20–30 mm to account for cable bend and your hand during install.
- Height and width: Most cases list this by form factor, but a quick check won’t hurt if a shroud or bracket sits tight.
- Fan side intake: If the PSU mounts at the bottom, check for a dust‑filtered vent. No vent? Flip the fan up into the case.
- Cable exits: Note where modular jacks or fixed leads sit. Some units place them higher or lower, which can change how cables clear a shroud.
Cable Plug Room Matters
Modular jacks and thick GPU leads need space to curve without stress. Leave at least a finger’s width behind the plugs. Stiff 12VHPWR or 12V‑2×6 leads used on modern GPUs bend poorly; a short right‑angle adapter can help in a tight floor‑mounted bay. On SFX builds, short cable kits keep the interior tidy and reduce bundle bulge behind the tray.
Airflow Path And Fan Orientation
Bottom‑mounted PSUs usually breathe from below. A filtered floor vent feeds the fan while the PSU exhausts out the rear. If your case sits on carpet or has a solid floor, flip the PSU so the fan faces up and draws from inside air. Keep at least a few centimeters of space under the case feet so the floor vent isn’t choked.
Power Rating And Size Aren’t The Same Thing
Wattage does not tell you anything about fit. A 750 W SFX‑L can be shorter than a 550 W long‑body ATX. Vendors pick the internal layout, heatsink size, and fan, then shape the case around those parts. Use wattage to size for your load, and the spec sheet to size for your chassis.
When To Choose Each Form Factor
ATX For Roomy Cases
Pick ATX when you have space and you want cable reach and fan choices. Depth of 140–160 mm keeps clearance for bottom fans and front shrouds in many modern cases. If your case lists a limit, stay under it. Long units can block a shroud cutout or push into a front intake path.
SFX/SFX‑L For Compact Builds
Small cases often demand SFX. SFX‑L offers the same mount with a quieter 120 mm fan in many models. In a larger case, running SFX with a bracket opens room for front‑to‑back airflow, extra cables, and even a small front radiator in tight spots. Just check cable lengths; some SFX kits ship shorter leads.
TFX Or Flex ATX When The Case Requires It
These are niche shapes. Use them for a low‑profile desktop, thin client, or rack chassis that calls them out. Check the vendor drawing for the case; hole position and length can vary slightly by brand, and some cases expect a specific cooling orientation.
Standards And Reference Drawings
If you want the source drawings and mounting notes, see Intel’s current desktop guides. The ATX v3.0 design guide collects ATX, SFX, and related notes, and the SFX12V guidelines include size and mounting details for small form factor builds.
Common Dimensions At A Glance
The table below lists common shells and the sizes builders see often. Depth can shift by model. Treat these as ballpark numbers and match them to your case spec.
| Form Factor | Typical Size (W×H×D, mm) | Common Fit |
|---|---|---|
| ATX | 150 × 86 × 140–200+ | Mid‑tower and full tower PSU bays |
| SFX | 125 × 63.5 × ~100 | Mini‑ITX and compact micro‑ATX cases |
| SFX‑L | 125 × 63.5 × ~130 | SFF cases that allow longer SFX depth |
| TFX | 85 × 65 × ~175 | Low‑profile desktops with slim bays |
| Flex ATX | 81.5 × 41 × ~150 | Compact 1U racks and tight OEM chassis |
Clearance Traps That Catch Builders
Shrouds And Drive Cages
Many modern cases hide the PSU behind a shroud. That shroud can pinch cable space near the modular panel. A unit deeper than 160 mm may bump into the shroud lip or a drive sled. If the case allows, slide the cage forward or remove one bay. If not, pick a shorter unit or swap to SFX with a bracket.
Bottom Fans And Radiators
A long PSU can block a bottom intake or force a slim fan choice. If you plan a bottom radiator, keep the PSU short and route cables before you mount the rad. On a compact case, SFX makes this far easier.
Right‑Angle Adapters And Bend Radius
New GPU plugs draw more current and ship with thick jackets. They don’t like sharp bends. Leave extra room behind the card and the PSU so the bundle can curve gently. A low‑profile 90‑degree adapter at the GPU can free space inside small enclosures, but make sure it’s certified and seats cleanly.
Noise, Thermals, And Fan Size
Shell size changes fan options. ATX units often use 120 mm or 135 mm fans. SFX tends to use 92 mm, while SFX‑L usually moves up to 120 mm. Bigger fans can spin slower at a given load, which helps with noise. Grid design on the intake and a straight airflow path also help, so keep cables clear of the fan face.
Modular, Semi‑Modular, Or Fixed Cables
Modular sockets add a few millimeters to depth and need plug room. In tight ATX bays, that plug depth can be the difference between a stress‑free bend and a kink. Fixed cable units are shorter but leave you with extra leads to hide. Semi‑modular strikes a balance by fixing only the 24‑pin and EPS leads.
Cable Length And Small Cases
SFX kits sometimes ship with shorter leads to reduce clutter. That helps in a small box but can come up short in a roomy mid‑tower. If you plan to run SFX in a larger case, check the cable list and add an extension for the EPS or GPU if needed. On the flip side, long ATX cables can clog a compact case. Tie off extra length and use the space above the PSU bay to stash bundles.
Adapters And Brackets That Make Life Easier
An SFX‑to‑ATX bracket is the most common helper and works in minutes. There are also brackets that offset the mount up or down to clear a shroud. Some cases include a sliding PSU frame so you can set depth before you tighten the screws. If your case has that frame, install the cables first, set the depth, then lock it down.
Warranty And Case Compatibility
PSU makers list form factor and depth in the specs, and case makers list maximum PSU length. Match those two lines and you’ll avoid returns. If a case lists a range “up to 180 mm without a bottom fan,” treat that as a hard limit. If you add a bottom fan later, shorten the PSU or move the fan.
Quick Build Checklist
- Confirm the form factor your case accepts: ATX, SFX, SFX‑L, TFX, or Flex ATX.
- Measure PSU depth room and reserve 20–30 mm for plug bend and fingers.
- Check bottom vent and filter. If the floor blocks air, face the fan up.
- Plan GPU cable routing and bend space for 12VHPWR or 12V‑2×6 leads.
- Use a bracket if you want SFX inside an ATX bay to gain airflow and space.
- Match cable length to case size. Add extensions only where you need them.
- Cross‑check case specs for “max PSU length” against the unit you plan to buy.
Clear Takeaway: PSU Sizes Aren’t One Size Fits All
Two power supplies can share a wattage and still fit in different ways. Form factor sets the rear opening and hole pattern; model depth, fan size, and plug layout change the rest. Measure the bay, give your cables breathing room, and pick the shell that suits the case. Do that, and the install will feel simple, clean, and safe.